1. Field of the Invention
The invention relates to a lens and an illumination device. More particularly, the invention relates to an illumination device having a lens with a light-incident structure.
2. Description of Related Art
A light emitting diode (LED) is a semiconductor device. The service life of the LED often exceeds a hundred thousand hours, and the LED does not require idling time. Moreover, the LED has the advantages of fast response speed (about 10−9 seconds), compact size, low power consumption, low pollution, high reliability, capability for mass production, etc. Therefore, the application of the LED is fairly extensive, for example, mega-size outdoor display boards, traffic lights, cell phones, light sources of scanners and facsimile machines, illumination devices, and so forth.
Since the brightness and the light-emitting efficiency of the LED continue to increase, and mass production of the white LED succeeds, the LED has been gradually applied for illumination. The LED often serves as a point light source. However, the light source for illumination is required to cover a relatively large area in most cases. Hence, when the LED acts as an illumination device, a light-diffusing structure, e.g., a lens unit, is required for resolving the issue of overly concentrated light from the point light source.
FIG. 8 is a portion of a conventional illumination device having a lens unit. Here, the lens unit is a lens 120′ which is formed by removing the top portion of a cone. When light L1′ irradiates the sidewall of the lens 120′, the light L1′ is reflected to a reflective layer 140′. Nonetheless, the light L2′ reflected by the sidewall of the lens 120′ may be transmitted out of the reflective layer 140′ and thus cannot be utilized effectively. As a result, the conventional lens unit encounters the issue of low light utilization rate.